for high sierra use the last version of clover and copy kexts you need into the kexts/10.13 folder or the kexts/10.12 your smbios should work just fine and also if you are using an hdd, don't use apfs, or your system will be very slow, use apfs only on ssds and also i know you are the guy that have trouble getting to work the audigy 2 zs, i can tell to you that i have just put the kx audio driver kext into the kexts/other folder and it worked fine in high sierra without doing anything else
Clover does not give me the choice of Mac Pro 5,1. I have been using IMac 13,2. Have you gotten Audigy 2 zs to run on an HP Z400. with Clover and Sierra? High Sierra is working just fine. I have installed every OS X since El Capitan on the HP Z400.